Over the last several decades, propylene polymers have become of great importance in several end use applications. From packaging for consumer goods to automotive components, propylene polymers have demonstrated wide applicability. Useful propylene polymers may generally be produced using Ziegler-Natta catalysts comprising 1) a solid titanium catalyst component consisting of a titanium compound, a magnesium compound, and an internal electron donor; 2) a co-catalyst such as an organoaluminum compound, and 3) external electron donors. The art is full of attempts of variations and specific combinations of the aforementioned catalyst components. The art has recognized that such variations and combinations are both unpredictable but advantageously influential on polymer properties. Therefore, the discovery of more variations and combinations of external electron donors, among other components, to accompany solid titanium catalyst has been of great benefit to improving the efficiency of the catalyst systems and the control of the polymer properties.
For example, external electron donors are used to control the stereoregularity and form of the polymer. Although a broad range of compounds are known generally as electron donors, a particular catalyst may have a specific compound or combinations of compounds with which it is especially compatible. Discovery of an appropriate type of electron donor can lead to significant improvements in the properties of the polymer such as molecular weight distribution and melt flow rate. Discovery of specific electron donors or combinations thereof for solid titanium based supported catalysts that would provide beneficial results would be highly advantageous in certain applications. Among these electron donors, organosilicon compounds, siloxanes or silanes have been of particular interest.
In particular, U.S. Pat. No. 6,376,628 and JP 1999263805A disclose the use of bis(perhydroisoquinolino)dimethoxysilane (BPIQ), among other catalyst components, in the polymerization of propylene. Other background references include CA 2 204 464, EP 0 841 348, JP 2001247617, JP 2001240634, JP 2001106717, JP 2000336113, JP 2000186110, JP 2000186109, JP 2000063419, JP 2000063417, JP 2000034313, JP 2000017009, JP 11349620, JP 11322830, JP 11269219, JP 11147906, JP 11147923, JP 11106434, JP 10292008, JP 10231316, JP 08143621, and JP 11106434. However, the art has yet to address every combination of BPIQ with other electron donors with certain catalyst systems to achieve a good balance of polymer properties.
The present invention fulfills this need by providing for catalyst systems and polymerization processes including electron donors including a mixture of a diaminodialkoxysilane, such as BPIQ, and a tetraalkoxysilane, such as tetraethoxysilane, or a trialkoxysilane, such as propyltriethoxysilane, in combination with a solid titanium catalyst system. Such combinations advantageously provide for a better balance of propylene polymer properties as can be observed, for example, through broad molecular weight distributions and wider ranges of desirable MFRs.